How to use realtime reflection probe in custom surface shader (Deferred Rendering)?

Is there a way to assign a reflection cube in the inspector? Is there an input type for them? I have the object set up to use it in its renderer, but in deferred rendering, it does not work I'm aware. But how to MAKE it work?

How can I for example use this unity example of fragment reflection as a surface shader?

 Shader "Unlit/SkyReflection"
 {
     SubShader
     {
         Pass
         {
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #include "UnityCG.cginc"
 
             struct v2f {
                 half3 worldRefl : TEXCOORD0;
                 float4 pos : SV_POSITION;
             };
 
             v2f vert (float4 vertex : POSITION, float3 normal : NORMAL)
             {
                 v2f o;
                 o.pos = UnityObjectToClipPos(vertex);
                 // compute world space position of the vertex
                 float3 worldPos = mul(_Object2World, vertex).xyz;
                 // compute world space view direction
                 float3 worldViewDir = normalize(UnityWorldSpaceViewDir(worldPos));
                 // world space normal
                 float3 worldNormal = UnityObjectToWorldNormal(normal);
                 // world space reflection vector
                 o.worldRefl = reflect(-worldViewDir, worldNormal);
                 return o;
             }
         
             fixed4 frag (v2f i) : SV_Target
             {
                 // sample the default reflection cubemap, using the reflection vector
                 half4 skyData = UNITY_SAMPLE_TEXCUBE(unity_SpecCube0, i.worldRefl);
                 // decode cubemap data into actual color
                 half3 skyColor = DecodeHDR (skyData, unity_SpecCube0_HDR);
                 // output it!
                 fixed4 c = 0;
                 c.rgb = skyColor;
                 return c;
             }
             ENDCG
         }
     }
 }